A few years ago our doctor hired a PA, and since then we've been billing her services incident-to because the doc has always been the first to see the patients, do the H/P, determine diagnosis and treatment plan, and is always in the office while the PA is seeing patients. Now we want to start having our PA see new patients (who will eventually see the doc). So this is about billing for an initial visit with the PA, which obviously can't be incident-to. My question is this: do I put the PA's NPI as rendering provider AND billing provider, or do I still use our practice NPI for the billing provider?

The rendering provider is the PA NPI, and the billing provider is the practice NPI, normally.

That was my thought (and hope), too. I know this varies from insurance to insurance, but if I'm using the PA as the rendering provider, but using our practice NPI as the billing provider, generally would we need a separate contract for the PA? I'm finding it surprisingly difficult to get that answered by contracting reps at various insurance companies.

Is linking the PA to the group done at each individual insurance carrier? Do you also add the practice as the PA employer at NPPES?

Yes, each individual carrier needs to be notified. Some may not require anything, but you need to check. If the PA is only practicing at the one location that should be the practice location indicated on their NPI through NPPES.